Method for the transportation and maintenance of a normally gaseous hydrocarbon in solution with a liquid hydrocarbon



1366- 1962 J. c. ALLEN ,068,657

METHOD FOR THE TRANSPORTATION AND MAINTENANCE OF A NORMALLY GASEOUSHYDROCARBON IN SOLUTION WITH A LIQUID HYDROCARBON Filed July 24, 1959 3Sheets-Sheet 1 A x w 1 k a k '1; N

Q A: k. (g 5% l k i T 1 3.1 b. ow4=e X/PROPULS/ON ,vS ECT/ON Dec. 18,1962 J. C AL METHOD FOR THE TRAN OF A NORMALLY SOLUTION WIT Filed July24, 1959 H A LIQUID HYDROCARBON 3 Sheets-Sheet- 2 LEN 3,068,657SPORTATION AND MAINTENANCE GASEOUS HYDROCARBON IN Dec. 18, 1962 J. c.ALLEN 3 METHOD FOR THE TRANSPORTATION AND MAINTENANCE OF A NORMALLYGASEOUS HYDROCARBON IN SOLUTION WITH A LIQUID HYDROCARBON Filed July 24,1959 s Sheets-Sheet s N u 20 l 9 0 p.574 3' \4 1o 0 I I I I I 0 2o 40 6a00 mo United States Patent This invention relates generally to themaintenance of a normally gaseous hydrocarbon in solution with a liquidhydrocarbon and, in one specific aspect, is concerned with a method forthe transport of a gaseous hydrocarbon, such as propane or some otherpetroleum gas, while dissolved in a liquid hydrocarbon, such as crudeoil or refined liquid petroleum products, at reduced temperatures.

Among the problems encountered in petroleum production and especially inforeign producing operations is that of the release of large quantitiesof petroleum gases,

which include the butanes, propane, ethane and methane.

Not only are these gases suitable for use in petrochemical productionand for fuel purposes, but also they are a valuable source, with butslight processing, for the enrichment of manufactured gas to be used forheating purposes. In domestic oil field production, the transportationof petroleum gases to the points of utilization is largely by means ofpipelines.

The shipment of liquefied petroleum gases for considerable distances isfeasible in containers which are built to withstand elevated pressures.However, the cost of manufacture of such containers, due to the amountand quality of material required, as well as the expense oftransportation of the heavy containers, restrict shipment to localizedregions. At the same time, because of the maximum allowable metal wallthickness permitted without stress relief, the size of such containersis limited.

Other means for transporting liquefied petroleum gases at lowtemperature and at substantially atmospheric pressure, include the useof insulated tanks mounted on barges or in vessels, the tanks beingconsiderably larger than the pressurized containers and employing balsawood for insulation. Because of the amount of such insulation required,the usable dimensions of the tank container are reduced considerably. Inaddition, there is the danger of low temperature embrittlement of carbonmight occur, should the insulation drop off. In the absence of the useof high cost alloy steels for constructing the tanks, the shipment ofliquefied petroleum gases is restricted by safety standards to therelatively heavier petroleum gases, such as the butanes and propane,which have the higher boiling points.

Among potentially prolific world sources of petroleum gases are those ofthe Middle East and of the South American oil fields adjoining theCaribbean Sea. In these regions, the production of petroleum gases couldbe lavish, but since they cannot be exploited fully, either by furtherprocessing or by shipment through pipelines to areas where such could beaccomplished, they are, in the case of a natural gas reservoir, notproduced, and in the case of solution gas from oil reservoirs,conservation regulations prevent its exhaust to the atmosphere as waste.If such petroleum gases should become available economically toenergy-deficient areas, the deficiency in energy requirements would bereduced.

In the shipment of liquefied petroleum gases, problems arise as to thetransportation and storage of these gases at their atmospheric boilingpoints and the installation of containers for holding them at their lowliquid temperatures, While it is known to transport and store liquefiedgases, such as nitrogen and oxygen, in Dewar type containers of spacedinner and outer receptacles, the problems encountered in theconstruction of such type containers for the shipment of the amounts ofliquefied petroleum gases required to justify their economicaltransportation prevents the use of the same.

Accordingly, it is an object of the present invention to provide for amore efficient and economical maintenance of a normally gaseoushydrocarbon dissolved in a liquid hydrocarbon.

Still another object of the present invention is to provide an improvedapparatus for the transportation of a normally gaseous hydrocarbondissolved in a liquid hydrocarbon.

These and other objects, advantages and features of the presentinvention will become apparent from the following description of theinvention and by reference to the accompanying drawings wherein:

FIG. 1a is a diagrammatic plan view of part of a tanker for use in thetransportation of a solution of a normally gaseous hydrocarbon dissolvedin a liquid hydrocarbon;

FIG. lb is a elevation view of the tanker of FIG. la and showing part ofthe installation used for maintaining the solution at low temperature;

FIG. 2 is a diagram of the auto-refrigeration recycle structure used inthe practice of this invention; and

FIG. 3 is a graph showing solubility curves as a function of temperatureof a normally mixture dissolved in a liquid hydrocarbon.

The objects of my invention are achieved by the use of anauto-refrigeration recycle for maintaining at low temperature a solutionof a normally gaseous hydrocar bon with a liquid hydrocarbon.

Referring to the drawings, FIGS. la and lb disclose the aft portion of atanker, indicated generally at T, with the power and propulsion sectionsindicated respectively as P and P, the pump room including accessoriessuch as the refrigeration unit and adjoining fuel oil wing tanks beinglocated in the section indicated at U, and the cargo tankage for crudepetroleum and refined products in a ble hull, indicated at H.

While all parts of the cargo tankage are suitable for the carriage ofcrude petroleum and petroleum products, for more efficient practice ofthe invention, it is preferable to provide the center tanks at C withthe mixture of 'In this manner, the surrounding exterior tanks serve toinsulate the outer walls of the tanker from the low temperature of therefrigerated solution.

Referring to FIG. 2, there cally a number of center tanks C holding asolution M As the solution absorbs heat, there is a continuous evolutionof the petroleum gas, which is drawn off through the headers 10 to amanifold ventional manner, the intake pump for the coolant being at 14and the outlet at 15. The liquefied petroleum gas, under high pressure,is directed to manifold 16, to which gaseous hydrocarbon are joined thetake-offs 17 leading to individual expansion valves 18, which areconnected to evaporator coils indicated at 19 and located adjacent thebottom of the center tanks C, or alternately connected to a distributorindicated as 19'. As the liquefied gas passes through the expansionvalves, and it's pressure is reduced, it changes from liquid to gaseousstate and cools the solution. Each of the coils 19'has at least onebleed valve, as at 20 (and alternatively the distributor has orifices20') for'release of the expanded gases into the solution. In thismanner, the'auto-refrigeration cycle maintains the temperature of thesolution at a low level and liquefied petroleum gas is added to and keptin solution. While the liquefied petroleum gas and liquid hydrocarbonsolution may be kept atatmospheric pressure, Coast Guard regulationspermit grade A cargo carriers to operate at a pressure below 1( gauge.

FIG. 3 presents solubility curves showing the great increase insolubilities of a 50-50 propane-butane mixture in normal octane as thetemperature of the solution is reduced. Octane is taken asrepresentative of the average properties of a liquid hydrocarbon. Thesecurves at atmospheric and l# gauge pressures indicate an approximate 300percent increase in solubilities as the ambient temperature of thesolution is lowered from about 80 F. to about 20 F.

Thus, there has been shown and described a method for the maintenanceand transportation of a normally gaseous hydrocarbon dissolved in aliquid hydrocarbon at low temperature and at about atmospheric pressure.

Obviously, many modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore 4 only such limitations should be imposedas are indicated in the the appended claim.

I claim:

The method of transporting a normally gaseous hydrocarbon atsubstantially atmospheric pressure and at reduced temperature comprisingthe solution of said normally gaseous hydrocarbon in a normally liquidhydrocarbon and the maintenance of the resulting solution at a reducedtemperature by auto-refrigeration comprising the drawing off of gaseoushydrocarbon evolved from said resulting solution, compressing the drawnoli evolved gaseous hydrocarbon to liquefaction, and passing theliquefied gaseous hydrocarbon in 'heat exchange relationship With saidsolution by bleeding ofi said liquefied gaseous hydrocarbon into saidsolution for dissolution therein whereby a reduced temperature isobtained to maintain said gaseous hydrocarbon in solution in said liquidhydrocarbon, said liquid hydrocarbon being chosen from the classcomprising crude petroleum and petroleum products.

References Cited in the file of this patent UNITED STATES PATENTS541,462 Suckert -a June 25, 1895 1,444,665 Crommett Feb. 6, 1923 1,98.95? Davenport Jan. 8, 1935 2,231,500 Harlow Feb. 11, 1941 2,217,138Newton Mar. 24, 1942 2,290,839 White a July 21, 1942 2,535,148 MartinDec. 26, 1950 2,550,886 Thompson May 1, 1951 2,933,902. Howard Apr. 26,1960 2,959,928 Maker Nov. 15, 1960

